Radio frequency transmission line



Sept. 19, 1939. H. o. PETERSON RADIO FREQUENCY TRANSMISSION LINE Filed sept. 9, 1935 ww m w n w w w QQSQE RSQ INVENTOR mm1/mcy f/v M55/:Crais H-O- PETERSON )l ATTORNEY Patented Sept. 19, 1939 UNITED STATES PATENT OFFICE Harold 0. Peterson, Riverhead, N. Y., assignor to Radio Corporation of America. a corporation of Delaware Application September 6 Claims.

This invention relates to an improved radiofrequency transmission line.

An object of this invention is to provide an improved transmission line comprising two conduc- 5 tors spaced apart from each other and arranged to have a deflnite ratio of spacing, and the diameter of metallic conductors and insulation to form an improved radio-frequency cable.

Another object of this invention is to provide an improved, Ainexpensive and convenient type of radio-frequency transmission cable which is particularly adapted for outdoor use, or where the cable is subjected to dampness.

Although radio-frequency transmission cables are old in the art, such cables have been found to give fairly satisfactory results during dry weather, but do not give satisfactory results during rainy weather or when used in damp locations.

I have found, upon close examination of such cables, that moisture seems to get in through the small pores in the fabric and its presence in the space between the wires causes an increase of signal attenuation. This moisture also causes a slight change in the characteristic surge impedance, which gives unsatisfactory results. Also I have found that after a period of rainy weather it takes several days for the transmission line to dry out before it recovers its normal operating characteristics.

By this invention I propose to maintain the normal dry weather operating characteristic impedance and attenuation of the transmission line at all times regardless of the moisture content of the surrounding atmosphere by careful selection of the diameters and spacing of the conductors for a given frequency, and also by applying a special waterproof coating around the conductors.

This invention will be best understood by referring tothe accompanying drawing, in which Fig. 1 shows an elevation of the improved radiofrequency transmission line;

Fig. 2 is an enlarged cross-section of the transmission cable;

Fig. 2a is a modification of Fig. 2; and

Fig. 3 shows a typical wet weather attenuation curve of a cable before and after waterproofing according to the invention.

Referring now to Figs. 1 and 2, the transmission line is shown composed of two #12 or #14 B. & S. gauge copper conductors l, which are arranged in parallel relationship and spaced apart from each other by an ordinary rubber coating 2. The spacing and insulation ratio for a given surge 9, 1935, 'serial No. 39,727

impedance of about 75 ohms I have found to be according to the following formula:

=substantially 0.24

wherein a is the radius of the conductor, and c spacing of the conductors, between centers. For almost all practical purposes it can be said that the desired center-to-center spacing of the conductors is approximately four times the radius of the conductors. The distance c between the conductors is equal to two times the thickness of the ordinary rubber coatingbplus two thicknesses of Para rubber plus the diameter of one conductor. Outside the ordinary rubber coating 2, I propose to completely cover, by a special waterproof wall 3 of a very high-grade and durable resilient rubber, coating containing about seventy percent ordinary rubber and 30 percent Para rubber or pure gum rubber which has been carefully prepared to remove all moisture and any substance which might contain moisture, the coating being approximately equal to the thickness of b. An insulation binder 5, preferably of rubber, binds the conductors together at the desired spacing. The outside wall thickness of the binder 5 at d is made about the same as the wall thickness at b. In the modification shown by Fig. 2a, the coductors, after being properly spaced as mentioned in the above formula, are covered directly with a seamless waterproof coat of lowloss rubber. After this coating is placed over the wire, it is carefully tested to determine whether there are any holes or cracks in the outer covering. Outside the waterproof layer of rubber there is woven tough coating of fabric 4, such as cotton impregnated with Bakelite or phenol condensation varnish.

The curves of Fig. 3 show the vattenuation of a cable composed of two #14 rubber covered wires when exposed to moisture. Curve A shows the attenuation of a wire not made according to this invention.

Curve B shows the attenuation of the same size wire as curve A, which has been made according to this invention.

This invention is not to be limited to the modifications described in this specification except such limitations as are clearly imposed by the appended claims, for example, in some of the normal constructions it might be desired to twist the conductors together to form a twisted pair.

Having thus described my invention, what I claim is:

1. A radio frequency transmission line having a surge impedance of about seventy-five ohms which maintains normal dry weather high frequency operating characteristics at a desired operating frequency without an increase in signal attenuation when said transmission line is subjected to moisture, comprising two parallel arranged conductors, a coating of ordinary rubber surrounding each of said conductors, a second water-proof coating of resilient rubber containing not less than thirty percent Para rubber from which all moisture has been removed covering over said irst mentioned coating which surrounds each conductor, an insulating binder surrounding said second mentioned water-proof coatings for maintaining each conductor spaced from center-to-centerv at approximately four times the radius of said conductor;

2. A radio frequency transmission line having a surge impedance of about seventy-five ohms which maintains normal dry weather high frequency operating characteristics at a desired operating frequency without an increase in signal attenuation when said transmission line is subjected to moisture, comprising two parallel arranged conductors, a coating of ordinary rubber surrounding each of said conductors, a second water-proof coating of resilient rubber containing not less than thirty percent Para rubber from which all moisture has been removed covering over said rst mentioned coating which surrounds each conductor, an insulating binder surrounding said second mentioned water-proof coatings for maintaining each conductor spaced from center-to-center at approximately four times the radius of said conductor, and a cover of fabric outside said insulating binder.

3. A radio frequency transmission line having a surge impedance of about seventy-five ohms which maintains normal dry Weather high frequency operating characteristics at a desired operating frequency without an increase in signal attenuation when said transmission line is subjected to moisture, comprising two parallel arranged conductors, a coating of ordinary rubber surrounding each of said conductors, a second water-proof coating of resilient rubber containing not less than thirty percent Para rubber from which all moisture has been removed covering over said lrst mentioned coating which surrounds each conductor, an insulating binder surrounding said second mentioned water-proof coatings for maintaining each conductor spaced from center-to-center at approximately four times the radius of said conductor, and a fabric cover of cotton impregnated in a phenol condensation varnish outside said insulating binder.

4. A radio frequency transmission line having a surge impedance of about seventy-five ohms which maintains normal dry weather high frequency operating characteristics at a desired operating frequency without an increase in signal attenuation when said transmission line is subjected to moisture, means to prevent said increase in signal attenuation comprising two parallel arranged conductors, a coating of ordinary rubber surrounding each of said conductors, a second Water-rproof coating of resilient rubber containing Par. rubber from which all moisture has been removed covering over said first mentioned coating which surrounds each conductor, an insulating binder surrounding said second mentioned water-proof coatings for maintaining each conductor spaced from center-to-center at approximately four times the radius of said conductor.

5. A radio frequency transmission line having a surge impedance of about seventy-five ohms which maintains normal dry weather high frequency operating characteristic impedance and attenuation when said line is operated above a million cycles Without an increase in signal attenuation when said transmission line is subjected to moisture, comprising two parallel arranged conductors, a coating of ordinary rubber surrounding each of said conductors, a second water-proof coating of resilient rubber containing not less than thirty percent Para rubber from which all moisture has been removed covering over said first mentioned coating which surrounds each conductor, an insulating binder surrounding said second mentioned water-proof coatings .for maintaining each conductor spaced from center-to-center at approximately four times the radius of said conductor;

6. A radio frequency transmission line having a surge impedance of about seventy-five ohms which maintains normal dry weather high frequency operating characteristic impedance and attenuation when said line is operated between three million and fifteen million cycles without an increase in signal attenuation when said 1 transmission line is subjected to moisture, comprising two parallel arranged conductors, a coatV ing of ordinary rubber surrounding each of said conductors, a second water-proof coating of resilient rubber containing not less than thirty percent Para rubber from which all moisture has been removed covering over said first mentioned coating which surrounds each conductor, o

an insulating binder surrounding said second mentioned water-proof coatings for maintaining each conductor spaced from center-to-center at approximately four times the radius of said conductor.

HAROLD O. PETERSON. 

